The proposed research is designed to provide quantitative data relating the effects of insonation of prenatal and juvenile rats to the intensity of the ultrasonic energy. Exposures will be made to graded time-intensities of ultrasound at representative times of gestation and of postnatal development. Three types of frequency-pulse conditions, which are representative of pulse-echo, Doppler, and diathermy techniques will be used. Detailed characterization of the ultrasonic beams will be made, and attempts will be made to estimate the energy absorbed by the conceptus. Some animals exposed will be sacrificed at 20 days of gestation; prenatal mortality is noted, and the fetuses examined in detail for the presence of malformations. To study the genesis of lesions which have been found in previous studies, other rats will be killed serially after exposure. In other experiments the animals will be allowed to deliver and the incidence of mortality and gross anomalies of the offspring determined. The growth and development of the offspring will be studied with particular emphasis on neurological, behavioral, or reproductive deficits, or in some cases, on the cardiovascular sytem. Other experiments will utilize juvenile rats, as a model for studying the potential for effects associated with fetal monitoring. Since effects have been observed at higher intensities, experiments will be performed to establish the biological mechanisms involved and to evaluate the role of ultrasonic exposure factors on the "dose-effect" relationship. The incident and absorbed energies associated with various clinical procedures will be estimated. These values will be compared with the "dose-effect" relationships and threshold estimates obtained from these experiments. These will allow an analysis of the safety and/or hazard associated with current clinical techniques.